Hermetic motors



United States Patent 3,514,652 HERMETIC MOTORS Michael J. Lacy, Florissant, and Jack D. Smith, Wentzville, Mo., assignors to Emerson Electric Co., St. Louis, Mo., a corporation of Missouri No Drawing. Filed Feb. 25, 1969, Ser. No. 802,197 Int. Cl. H02k 1/18 U.S. Cl. 310-217 3 Claims ABSTRACT OF THE DISCLOSURE In an electric motor assembly of the type in which a wound stator With a core made up of a stack of laminations is bolted in face-to-face relation to a base made of an electrically conductive material, the bolts go entirely through the stack of laminations and into the base; the underside of the head of the bolts and at least a substantial portion of the shank of the bolts are coated with a metal oxide deposited by flame or plasma spraying to form a suitably electrically resistive layer.

BACKGROUND OF THE INVENTION It has been discovered that in so-called hermetic motors, in which a wound stator with a core made up of a stack of laminations is bolted in face-to-face relation to a cast metal base, the throughbolts in the conventional arrangement lowered the motor efliciency because an electric current has been induced in the bolts, which passes through the bolts, the base, and the laminations with which the bolt head comes in contact, to form an electrical circuit. The problem and its general solution are discussed in a pending application of Robert M. Vreeland, Ser. No. 556,140, now Pat. No. 3,447,010. Insulation of the bolt head from the surface of the lamination upon which it bears can be accomplished in a number of ways. In Vreeland, the means used is a fiber washer, which, Vreeland points out, may be laminated with one or more metal washers. An application of Robert L. Harris, Ser. No. 607,410, now Pat. No. 3,428,842, discloses an improved form of laminated washer, which also serves as a bolt centering device. While the use of. a washer is satisfactory, it does require a separate part, and thus increases the labor and expense of accomplishing Vreelands object, and does not provide positive insulation of the throughbolt along the axial reach of the core.

One of the objects of this invention is to provide an assembly in which an integrious insulator is made integral with the underside of the head, and at least a portion of the shank of the throughbolts, to provide a more efficient motor assembly than has been provided heretofore, inexpensively.

Other objects will become apparent to those skilled in the art in the light of the following description.

SUMMARY OF THE INVENTION In accordance with this invention, generally stated, in a motor assembly in which a core made up of a stack of laminations is bolted in face-to-face relation to a base made of an electrically conductive material, throughbolts are provided on the underside of the head and on the shank of which a metallic oxide has been bonded by flame or plasma spraying. The term integral is used herein to describe the relation of the bolt and coating. As described in a bulletin of Union Carbide Corporation en- 3,514,652 Patented May 26, 1970 titled Plasma-Plating, the coating material forms a highdensity layer, producing a microscopic weld which for practicalpurposes actually becomes part of the substrate. Similarly, the coating produced by flame plating or flame spraying is said to be welded to the base material, of. brochure identified as Linde Flame-Plating of Union Carbide Corporation. Suitable equipment for such coating is offered by Metco, -Inc., as described in that companys Bulletins 177, 178 and 179.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the preferred embodiment of motor of this invention, the underside of the head of the throughbolts, and all of the part of the shank of the throughbolts which does not engage the threads of a tapped hole in the base into which the throughbolt is screwed, are coated with aluminum oxide of 99% purity, having a cross-sectional hardness of approximately 1100 VPN, a modulus of rupture of 20,000 p.s.i., a modulus of elasticity of 5.7 l0 p.s.i., a porosity of 3%, a specific gravity of 3.32 gm./cc., and a thermal conductivity of 1.7 at 200 F. and 3.3 at 500 F. A suitable coating material is designated by Union Carbide Corporation as LA-6.

It has been found that contrary to what might have been expected, it is not necessary to provide the substantially absolute electrical insulation of a fiber washer, for example. A coating of aluminum oxide of the character described six mills thick will produce sufiicient electrical resistivity to inhibit effectively the flow of current through the throughbolts. The coating on the underside of the bolt head has sufficient mechanical resistance to shear forces to withstand the forces generated in the turn down of the bolts, and the coating on the bolt shank is sufliciently resistant to the abrasion of any edges of the laminations with which it comes in contact to remain, like the coating on the underside of the bolt head, integrious in assembly.

. The aluminum oxide coating of the preferred embodiment is inexpensive and highly efiicient. For other appli cations or different conditions of use, other oxides may be utilized, such as titanium oxide (TiO either alone or in combination with aluminum oxide, chromium oxide (Cr O either alone or in combination with aluminum oxide (A1 0 or zirconium oxide (ZrO Ceramic coatings, as, for example, a water slurry of borofluoro hydroxy carbosilicate applied to the bolts and baked, have been tried and while the coatings provide electrical insulation when unbroken, they are inferior in mechanical strength and reliability to the plasma and flame coatings described.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1. In a hermetic motor in which a laminated stator is bolted in face-to-face relation to a base of electrically conductive material by means of throughbolts each having a head and a shank portion the end opposite the head of which is threaded into a tapped hole in the said base, the improvement comprising said throughbolts having an integrious metal oxide coating integral with the underside of the head and at least a part of the shank adjacent the head, said coating having an electrical resistivity substantially to inhibit a flow of current between the said throughbolts and the said stator.

2. The improvement of claim 1 wherein the metal 4 oxides are taken from the group consisting of aluminum 3,170,735 2/ 1965 Coflin 174-152 XR oxide, titanium oxide, chromium oxide and zirconium 3,447,010 5/1969 Vreeland 310 -217 oxide, and are applied to said throughbolts by means of 3,428,842 2/1969 Harris 310217 one of flame and plasma spraying.

3. The improvement of claim 1 wherein the oxide is 5 L O 0 HIRSHFIELD, primary Examiner aluminum oxide and the coating is at least six mils thick, B. A. REYNOLDS, Assistant Examiner References Cited UNITED STATES PATENTS 2,326,455 8/1943 Gray. 10 29-596; 85-1; 174-110; 310 -218, 259 3,109,053 10/1963 Ahearn "174-1101 3,259,818 7/1966 Garstang et al. 174110.1 XR 

